>
>In the common circuit used for GG triode amplifiers that separates the B-
>from
>ground in order to allow for convenient plate and grid current metering,
>there
>is a 'safety resistor' from B- to ground.
>
>Most designs seem to use a value like 10 or 20 ohms. As G3sek
><http://www.ifwtech.demon.co.uk/g3sek/> points out, if you use the 'voltmeter
>method' to measure grid current, the high value of the shunt resistor
>requires a
>higher value for the safety resistor (he suggests 1000 ohms) to keep the grid
>metering accurate.
>
>My question is: What malfunction is this 'safety resistor' protecting us
>against?
? Destructive surge current, provided that the resistor is installed
where it belongs.
>What could happen if it were omitted or opened in service?
>
? This resistor belongs in the positive side of the hv supply, not the
negative. When the glitch resistor is in negative circuitry, a positive
to gnd arc elevates the cathode circuitry to many kilovolts. A glitch
resistor needs to be stout enough to withstand repeated hv positive to
gnd arcs.
- Rich..., 805.386.3734, www.vcnet.com/measures.
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